1. Field of the Invention
The present invention relates to a technique for manufacturing a silicon carbide semiconductor device.
2. Description of the Background Art
In order to break the limitation of properties of power devices using silicon, development of power devices using silicon carbide has been made. Especially, p-type ohmic contact of low resistivity is an essential element for a silicon carbide semiconductor device and in order to achieve it, it is very important to establish a technique for forming a high-concentration p++ layer.
In a method of forming a p-type base ohmic contact shown in Japanese Patent Application Laid Open Gazette No. 2007-66959 (Patent Document 1), for forming a p++ layer for contact, ion implantation (Al, B, Ga) is performed under an atmosphere of the temperature of 400° C. or higher and this makes it possible to avoid any process failure occurring in manufacture of silicon carbide MOSFETs.
Further, Japanese Patent Application Laid Open Gazette No. 2007-227655 (Patent Document 2) discloses that silicon carbide is heated up to 150° C. to 400° C. during high-concentration ion implantation and this suppresses crystal degradation due to the ion implantation.
Since the silicon carbide has better property value than silicon, the silicon carbide is expected as a semiconductor material for next-generation power devices. A p-type base ohmic contact of a MOSFET using silicon carbide consists of a p++ layer formed by implantation of high-concentration ions (Al, B, Ga) having a concentration of 1e19 cm−3 to 1e21 cm−3 and a metal electrode. Since the crystal of the p++ layer is significantly degraded when implantation of such high-concentration ions is performed at room temperature, this causes a process failure in manufacture of devices. Therefore, the method of performing the high-concentration ion implantation at high temperatures to suppress the crystal degradation is used.
On the other hand, in terms of switching loss, avalanche capability and the like of devices, it is desirable that the resistivity of the p-type base ohmic contact should be lower.
In well-known techniques, however, nothing is mentioned on a detailed relation among the temperature for high-concentration ion implantation, the resistivity of a p-type base ohmic contact and the process failure in manufacture of devices.